feat(game): add persistent bush-wall breakthroughs

PLANS.md

@@ -2271,7 +2271,7 @@ The following planning-time observation motivated the milestone:
 
 ## Milestone 022 — Persistent bush-wall breakthrough
 
-**Status:** `NOT_STARTED`
+**Status:** `COMPLETE`
 
 ### Objective
 
@@ -2426,3 +2426,149 @@ The following planning-time decisions define this milestone:
   always available to both players.
 - Implementation, automated verification, physical-device checks, and owner
   acceptance are deferred until all preceding milestones are `COMPLETE`.
+- 2026-09-10 implementation evidence: `bash scripts/run_host_tests.sh` passed,
+  including `game persistent bush-wall breakthrough: PASS (five impacts, shared
+  passage)`. `node --test test/web/test_player_app.js` passed all 23 browser
+  tests and confirmed the bounded impact and trampled-passage presentation.
+
+## Milestone 023 — Top-down living hedge SVG sample library
+
+**Status:** `NOT_STARTED`
+
+### Objective
+
+Design and obtain project-owner approval for a lightweight SVG sample library
+that makes maze walls read as varied living hedges viewed from above, with
+recognizable leaves, twigs, depth, and matching damaged and permanently
+breached variants for perseverance mode, without integrating the artwork into
+the running game in this milestone.
+
+### Scope
+
+- Do not start this milestone until every preceding milestone is `COMPLETE`.
+- Treat this as a visual exploration and asset-approval milestone only. Do not
+  replace the current maze renderer, change gameplay, modify the protocol, or
+  ship the samples in browser or firmware assets during this milestone.
+- Before drawing, add a concise hedge-art contract to `docs/UI_STYLE.md` that
+  defines top-down perspective, scale, palette, outline weight, contrast,
+  organic variation, tiling rules, and the relationship between intact,
+  impacted, and permanently breached bushes.
+- Create editable, hand-reviewable SVG source artwork with semantic groups and
+  stable symbol identifiers. Do not embed raster images, external fonts,
+  remote resources, scripts, generated metadata, or tool-specific binary data.
+- Explore at least six visibly different intact straight-hedge samples. Vary
+  leaf clusters, branch paths, gaps, highlights, and silhouette rhythm while
+  keeping every sample unmistakably part of one visual family.
+- Include representative joins and boundary situations needed by a cell-based
+  maze: continuous straight runs, perpendicular corners, crossings of adjacent
+  wall segments, exposed ends, and shared edges. Samples must rotate or mirror
+  cleanly for all four cardinal directions without directional lighting errors.
+- Make individual leaves and small branch forks distinguishable at the actual
+  supported maze scales of 34, 40, and 46 CSS pixels per cell. Avoid both flat
+  green bars and noisy texture that turns into visual static on a phone.
+- Use at least three vegetation tones plus restrained branch and shadow tones
+  to create depth. Maintain an identifiable hedge silhouette without relying
+  on green hue alone and keep players, keys, doors, passages, and interactive
+  feedback visually dominant.
+- Draw a coherent perseverance sequence for the same representative wall:
+  intact, four increasing impact stages, the moment of breakthrough, and the
+  final permanent trampled opening. Branch bending, displaced leaves, broken
+  twigs, compressed foliage, and the cleared center must evolve consistently
+  rather than appearing as unrelated pictures.
+- Provide at least three final breached-hedge samples with different organic
+  edge shapes. Each must clearly show a traversable gap from a top-down view,
+  retain torn or flattened bushes on both sides, and remain recognizable when
+  rotated or mirrored.
+- Keep openings visually aligned to the authoritative cell passage and wide
+  enough for the player icon without implying a larger traversable area. The
+  samples must not encode coordinates, hidden passages, objects, ownership, or
+  other game state.
+- Present all concepts together on one neutral comparison sheet and also as
+  isolated SVG symbols on representative dark maze cells. Include previews at
+  1x and high-density mobile rendering scales, with no smoothing assumptions
+  that are unavailable in ordinary browsers.
+- Record approximate raw and compressed byte costs for each candidate family
+  so later integration can select variety without threatening the 1.5 MiB web
+  asset budget or LittleFS partition. Prefer reusable leaf, twig, shadow, and
+  damage components over repeated paths where that improves size and clarity.
+- Check color-vision robustness, grayscale silhouette, normal contrast, and
+  reduced-motion suitability. This milestone defines static frames only;
+  animation timing and runtime particle behavior remain governed by Milestone
+  022 and are outside this milestone's implementation scope.
+- End with an explicit project-owner selection of the preferred intact hedge
+  family, damage progression, breached variants, density, and palette. Runtime
+  integration requires a separately planned later milestone after approval.
+
+### Deliverables
+
+- Updated hedge-art and sample-review contract in `docs/UI_STYLE.md`.
+- Editable SVG symbol sheet containing intact straight segments, joins, ends,
+  four impact stages, breakthrough frame, and permanent breached variants.
+- Neutral comparison sheet plus representative dark-cell previews at 34, 40,
+  and 46 CSS pixel cell sizes and normal and high-density mobile scales.
+- Brief asset manifest describing symbol identifiers, reuse rules, rotation and
+  mirroring constraints, accessibility checks, and raw and compressed sizes.
+- Recorded project-owner selection and any requested revisions; no browser or
+  firmware integration changes.
+
+### Acceptance criteria
+
+1. The sample library contains at least six intact straight-hedge variants,
+   representative continuous runs, corners, shared-edge joins, and exposed
+   ends, all drawn as editable vector artwork with stable semantic identifiers.
+2. Every intact sample resembles a living hedge viewed directly from above and
+   contains clearly distinguishable leaf clusters and branching structure. No
+   candidate is merely a solid, gradient, or textured green bar.
+3. The candidates form one coherent visual family while showing enough
+   silhouette, foliage, branch, highlight, and gap variation to prevent obvious
+   repetition across a representative maze preview.
+4. Leaves and primary branch forks remain recognizable at 34, 40, and 46 CSS
+   pixel cell sizes at 1x rendering. At high density they gain clarity without
+   changing geometry, producing seams, or becoming disproportionately detailed.
+5. Straight segments, corners, joins, and ends connect without visible gaps,
+   doubled borders, accidental knots, or discontinuous lighting when rotated or
+   mirrored into every cardinal orientation.
+6. At least three vegetation tones plus restrained branch and shadow tones
+   provide top-down depth. Grayscale and representative color-vision checks
+   preserve the hedge silhouette and do not reduce the legibility of players,
+   keys, doors, passages, or feedback.
+7. One representative wall has a visually continuous set of intact, impact
+   stages one through four, breakthrough, and permanent-open frames. Each stage
+   shows plausible cumulative bending or damage and is distinguishable from
+   adjacent stages without explanatory text.
+8. At least three permanent breached variants show an unambiguous traversable
+   center with torn, bent, or flattened vegetation on both sides. They remain
+   understandable from either side after rotation or mirroring and do not look
+   like an intact or merely shadowed wall.
+9. Every breached opening aligns to one authoritative wall passage, is visually
+   wide enough for the existing player icon, and does not suggest access to an
+   adjacent closed cell or reveal any hidden maze state.
+10. SVG files contain no raster payloads, external dependencies, scripts,
+    unnecessary editor metadata, or unbounded duplication. The manifest records
+    raw and compressed size for each candidate family and identifies reusable
+    components.
+11. The comparison sheet shows all candidates on a neutral background and the
+    preferred candidates on representative dark maze cells at all target sizes.
+    Review does not require running or modifying the game.
+12. No runtime HTML, CSS, JavaScript, firmware, protocol, generated web bundle,
+    or LittleFS image changes are part of this milestone. Automated checks
+    confirm SVG validity, local-only dependencies, stable identifiers, and
+    deterministic optimization output.
+13. The project owner selects or explicitly rejects the intact hedge family,
+    impact sequence, breached variants, density, and palette after reviewing the
+    sample sheet at representative mobile scale. Any requested revisions are
+    recorded before the milestone can become `COMPLETE`.
+
+### Evidence
+
+The following planning-time request defines this milestone:
+
+- On 2026-09-10, the project owner requested a future sample-drawing milestone
+  because maze walls should look like varied living hedges from above rather
+  than simple green sticks. The owner specifically required visible leaves and
+  branches plus matching broken-bush samples for permanent breakthroughs in
+  perseverance mode, and requested planning only with no immediate artwork or
+  runtime implementation.
+- Artwork creation, review previews, validation, owner approval, and any later
+  runtime integration are deferred. Milestone 022 remains the sole active
+  milestone at planning time.